U.S. Pat. No. 4,956,043 discloses a device of the kind mentioned in the opening paragraph in which the wall of the cooling chamber formed by the lower side of the support plate is of stepped design. A plane central horizontally situated portion forms the first portion of the wall, and a higher horizontal plane edge forms the second portion which projects less far into the cooling chamber. During operation, liquid nitrogen is adjusted to such a level in the cooling chamber that the first portion of the wall is continuously in the nitrogen.
It is found in practice that substrates cannot be optimally cooled in the known device. When liquid nitrogen is used as the cooling liquid, the substrates do not reach the temperature of liquid nitrogen. This is particularly true when the substrates are heated by incident ions or other particles during the etching or deposition processes.